1. Field of the invention
The present invention relates to a control apparatus for an inverter-driven elevator, more particularly to an elevator control apparatus having an improved function for detecting a present position of a cage of the elevator.
2. Description of the related art
In an elevator control, it is one of the important factors that a cage of an elevator can land at the level of a floor accurately, and therefore a great concern has been paid about raising the landing accuracy as much as possible.
For this purpose, the speed of the cage is necessary to be controlled accurately. Particularly the high accuracy is required in the speed control during the deceleration of an elevator cage. In order to meet this, an inverter, which is controlled in accordance with a so-called vector control, has been used to control an induction motor for driving an elevator cage, because the vector control can achieve the accurate control of the speed of the induction motor.
Even with the vector control, however, it was still necessary to accurately detect the speed of a cage. Therefore, as disclosed, for example, in U.S. Pat. No. 4,600,088 (issued July 15, 1986), an expensive detector such as a rotary encoder has been employed in order to detect the speed of a motor or the present position of an elevator cage accurately.